U.S. patent application number 14/594560 was filed with the patent office on 2015-07-16 for image-forming apparatus for controlling speed of fan based on detected temperature.
This patent application is currently assigned to BROTHER KOGYO KABUSHIKI KAISHA. The applicant listed for this patent is BROTHER KOGYO KABUSHIKI KAISHA. Invention is credited to Shintaro SAKAGUCHI, Kaoru SUZUKI.
Application Number | 20150198918 14/594560 |
Document ID | / |
Family ID | 53521295 |
Filed Date | 2015-07-16 |
United States Patent
Application |
20150198918 |
Kind Code |
A1 |
SAKAGUCHI; Shintaro ; et
al. |
July 16, 2015 |
IMAGE-FORMING APPARATUS FOR CONTROLLING SPEED OF FAN BASED ON
DETECTED TEMPERATURE
Abstract
In an image-forming apparatus an image-forming portion performs
a printing operation in which an image is formed on a sheet. A
heater thermally fixes the image on the sheet. A processor is
configured to: determine whether a temperature detected by a
detector is higher than a threshold value before the image-forming
portion perform the printing operation; drive a fan at a first
speed following start of the printing operation when the
temperature is higher than the threshold value; and drive the fan
at a second speed lower than the first speed for a prescribed
period of time following the start of the printing operation when
the temperature is lower than the threshold value or equal to the
threshold, and subsequently drive the fan at the first speed;
control a temperature of the heater based on the temperature
detected by the detector while the image-forming portion performs
the printing operation.
Inventors: |
SAKAGUCHI; Shintaro;
(Nagoya-shi, JP) ; SUZUKI; Kaoru; (Ichinomiya-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BROTHER KOGYO KABUSHIKI KAISHA |
Nagoya-shi |
|
JP |
|
|
Assignee: |
BROTHER KOGYO KABUSHIKI
KAISHA
Nagoya-shi
JP
|
Family ID: |
53521295 |
Appl. No.: |
14/594560 |
Filed: |
January 12, 2015 |
Current U.S.
Class: |
399/69 |
Current CPC
Class: |
G03G 15/2017 20130101;
G03G 15/2039 20130101 |
International
Class: |
G03G 15/20 20060101
G03G015/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 16, 2014 |
JP |
2014-005985 |
Claims
1. An image-forming apparatus comprising: a fan; an image-forming
portion configured to perform a printing operation in which an
image is formed on a sheet; a heater configured to thermally fix
the image on the sheet; a detector configured to detect a
temperature of the heater; and a processor configured to: determine
whether the temperature detected by the detector is higher than a
threshold value before the image-forming portion perform the
printing operation; drive the fan at a first speed following start
of the printing operation when the temperature is higher than the
threshold value; and drive the fan at a second speed lower than the
first speed for a prescribed period of time following the start of
the printing operation when the temperature is lower than the
threshold value or equal to the threshold, and subsequently drive
the fan at the first speed; control a temperature of the heater
based on the temperature detected by the detector while the
image-forming portion performs the printing operation.
2. The image-forming apparatus according to claim 1, wherein the
processor is further configured to set the prescribed period of
time based on the temperature detected before the start of the
printing operation.
3. The image-forming apparatus according to claim 1, wherein the
processor is further configured to set the prescribed period of
time based on a printing speed of the image-forming portion.
4. The image-forming apparatus according to claim 1, wherein the
detector includes a non-contact temperature sensor configured to
detect the temperature of the heater without contact.
5. The image-forming apparatus according to claim 4, wherein the
processor is further configured to: change the detected temperature
to a corrected temperature by using a selected one of a plurality
of temperature correction formulae that is selected depending upon
the detected temperature; and control a temperature of the heater
based on the corrected temperature.
6. The image-forming apparatus according to claim 5, wherein the
temperature correction formula is set such that the lower the
detected temperature is, the greater a difference between the
detected temperature and the corrected temperature is.
7. The image-forming apparatus according to claim 5, wherein the
temperature correction formula is set such that the longer an
elapsed time from a moment when the heater starts generating heat,
the smaller a difference between the detected temperature and the
corrected temperature is.
8. The image-forming apparatus according to claim 1, further
comprising: a casing; and a cover configured to selectively cover
and expose at least a part of the casing, wherein the processor is
further configured to drive the fan at a constant speed following
the start of the printing operation when the cover exposes the at
least a part of the casing.
9. The image-forming apparatus according to claim 1, further
comprising a casing, wherein the fan controls an internal
temperature of the casing.
10. The image-forming apparatus according to claim 1, wherein the
image-forming portion configured to perform a printing operation
based on a print job; wherein the processor is further configured
to: receive a print job; determine whether the print job is
received or not; and obtain the temperature detected by the
detector in response to determine that the print job is
received.
11. An image-forming apparatus comprising: a fan configured to
drive at a first speed and a second speed that is lower than the
first speed; an image-forming portion configured to perform a
printing operation in which an image is formed on a sheet; a heater
configured to heat the image on the sheet; a non-contact
temperature detector configured to detect a temperature of the
heater without contact; and a processor configured to: drive the
fan at the second speed for a prescribed period of time following
the start of the printing operation and subsequently drive the fan
at the first speed; obtain the temperature detected by the
non-contact temperature detector when the fan drives; and control a
temperature of the heater based on the obtained temperature.
12. The image-forming apparatus according to claim 11, wherein the
processor is further configured to set the prescribed period of
time based on the temperature detected before the start of the
printing operation.
13. The image-forming apparatus according to claim 12, wherein the
higher the temperature is, the shorter the prescribed period of
time is.
14. The image-forming apparatus according to claim 12, wherein the
image-forming portion is further configured to include a
first-speed printing mode and a second-speed printing mode, a
printing speed of the second-speed printing mode being slower than
a printing speed of the first-speed printing mode; the prescribed
period of time in the first-speed printing mode is shorter than the
prescribed period of time in the second-speed printing mode.
15. An image-forming apparatus comprising: a fan configured to
drive a first speed or a second speed that is slower than the first
speed; an image-forming portion configured to perform a printing
operation in which an image is formed on a sheet; a heater
configured to heat the image on the sheet; a detector configured to
detect a temperature of the heater; a memory configured to store a
temperature correction formula; and a processor configured to:
obtain a speed of the fun; obtain a temperature correction formulae
from the memory based on the speed of the fun; correct the
temperature to a corrected temperature by using a obtained
temperature correction formulae; and control a temperature of the
heater based on the corrected temperature.
16. The image-forming apparatus according to claim 15, wherein the
temperature correction formula is set such that the lower the
detected temperature is, the greater a difference between the
temperature and the corrected temperature is.
17. The image-forming apparatus according to claim 15, wherein the
temperature correction formula is set such that the longer an
elapsed time from a moment when the heater starts generating heat,
the smaller a difference between the temperature and the corrected
temperature is.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from Japanese Patent
Application No. 2014-005985 filed Jan. 16, 2014. The entire content
of the priority application is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to a technique for controlling
a cooling fan used to cool the interior of an image-forming
apparatus.
BACKGROUND
[0003] Japanese Patent Application Publication No. 2005-148105
discloses a technique for controlling the internal temperature of
an image-forming apparatus. This image-forming apparatus uses a
built-in temperature sensor for detecting the internal temperature
and fan control based on the detected temperature data.
SUMMARY
[0004] However, when using a fan to cool the interior of an
image-forming apparatus based on temperature data detected with a
built-in sensor, as in the conventional device described above, the
fan operation may also affect the temperature in the fixing unit,
potentially leading to problems in the fixing operation.
[0005] In view of the foregoing, it is an object of the present
invention to provide a technique for controlling the fan in an
image-forming apparatus based on detection results from a
temperature-detecting unit that detects the temperature in the
fixing unit of the image-forming apparatus.
[0006] In order to attain the above and other objects, the
invention provides an image-forming apparatus. The image-forming
apparatus includes a fan, an image-forming portion, a heater, a
detector, and a processor. The image-forming portion is configured
to perform a printing operation in which an image is formed on a
sheet. The heater is configured to thermally fix the image on the
sheet. The detector is configured to detect a temperature of the
heater. The processor is configured to: determine whether the
temperature detected by the detector is higher than a threshold
value before the image-forming portion perform the printing
operation; drive the fan at a first speed following start of the
printing operation when the temperature is higher than the
threshold value; and drive the fan at a second speed lower than the
first speed for a prescribed period of time following the start of
the printing operation when the temperature is lower than the
threshold value or equal to the threshold, and subsequently drive
the fan at the first speed; control a temperature of the heater
based on the temperature detected by the detector while the
image-forming portion performs the printing operation.
[0007] According to another aspect, the present invention provides
an image-forming apparatus. The image-forming apparatus includes a
fan, an image-forming portion, a heater, a non-contact temperature
detector, and a processor. The fan is configured to drive at a
first speed and a second speed that is lower than the first speed.
The image-forming portion is configured to perform a printing
operation in which an image is formed on a sheet. The heater is
configured to heat the image on the sheet. The non-contact
temperature detector is configured to detect a temperature of the
heater without contact. The processor is configured to: drive the
fan at the second speed for a prescribed period of time following
the start of the printing operation and subsequently drive the fan
at the first speed; obtain the temperature detected by the
non-contact temperature detector when the fan drives; and control a
temperature of the heater based on the obtained temperature.
[0008] According to another aspect, the present invention provides
an image-forming apparatus. The image-forming apparatus includes a
fan, an image-forming portion, a heater, a detector, a memory, and
a processor. The fan is configured to drive a first speed or a
second speed that is slower than the first speed. The image-forming
portion is configured to perform a printing operation in which an
image is formed on a sheet. The heater is configured to heat the
image on the sheet. The detector is configured to detect a
temperature of the heater. The memory is configured to store a
temperature correction formula. The processor is configured to:
obtain a speed of the fun; obtain a temperature correction formulae
from the memory based on the speed of the fun; correct the
temperature to a corrected temperature by using a obtained
temperature correction formulae; and control a temperature of the
heater based on the corrected temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The particular features and advantages of the invention as
well as other objects will become apparent from the following
description taken in connection with the accompanying drawings, in
which:
[0010] FIG. 1 is a side cross-sectional view of a printer according
to a first embodiment of the present invention;
[0011] FIG. 2 is a block diagram showing an electrical structure of
the printer according to the first embodiment;
[0012] FIG. 3 is a graph illustrating a difference between an
actual temperature of the fixing unit and a temperature detected by
a thermistor according to the first embodiment;
[0013] FIG. 4 is a printer state transition diagram according to
the first embodiment;
[0014] FIG. 5A is a flowchart illustrating a part of a fan control
process according to the first embodiment;
[0015] FIG. 5B is a flowchart illustrating a remaining part of the
fan control process according to the first embodiment;
[0016] FIG. 6 is a printer state transition diagram according to a
second embodiment; and
[0017] FIG. 7 is a printer state transition diagram according to a
third embodiment.
DETAILED DESCRIPTION
[0018] A printer 1 according to a first embodiment of the invention
will be described while referring to FIGS. 1-5B. FIG. 1 is a side
cross-sectional view showing the relevant components of a printer
1. The printer 1 (an example of an image-forming apparatus)
includes a device frame 2 (casing), a sheet-feeding unit 4, an
image-forming unit 10, a fixing unit 40, and a fan 50. In the
following explanations, right side of FIG. 1 will be referred to as
front side, left side of FIG. 1 will be referred to as rear
side.
[0019] The sheet-feeding unit 4 includes a paper tray 5 that holds
sheets S of a printing paper, a lifting plate 6, and a feeding
roller 7. The lifting plate 6 is capable of pivoting about its rear
edge and presses the sheets S resting on top of the lifting plate 6
toward the feeding roller 7. The feeding roller 7 can rotate to
feed sheets S one at a time onto a conveying path.
[0020] A sheet S fed by the feeding roller 7 follows the conveying
path downstream to a pair of registration rollers 9. The
registration rollers 9 first correct skew in the sheet S relative
to the conveying direction and then convey the sheet S to a
transfer position X. The transfer position X is the position at
which a photosensitive drum 31 contacts a transfer roller 35 and at
which a toner image carried on the photosensitive drum 31 is
transferred to the sheet S.
[0021] The image-forming unit 10 functions to form a toner image on
the sheet S. The image-forming unit 10 includes a scanning unit 11,
and a process unit 21. The scanning unit 11 has a laser
light-emitting unit (not shown), a polygon mirror 12, and the like.
The laser light-emitting unit emits a laser beam (depicted by a
chain line in FIG. 1) that is deflected off the polygon mirror 12
and irradiated onto the surface of the photosensitive drum 31.
[0022] The process unit 21 includes a developing cartridge 23, the
photosensitive drum 31, and a scorotron charger 33.
[0023] The developing cartridge 23 includes a supply roller 24, a
developing roller 25, and a blade 26. A toner-accommodating chamber
27 is also formed inside the developing cartridge 23 for
accommodating toner as an example of the developer.
[0024] The supply roller 24 supplies positively charged toner from
the toner-accommodating chamber 27 onto the surface of the
developing roller 25. The developing roller 25 supplies the
positively charged toner onto the surface of the photosensitive
drum 31.
[0025] The scorotron charger 33 applies a uniform positive charge
to the surface of the photosensitive drum 31. The laser beam
emitted from the scanning unit 11 exposes the positively charged
surface of the photosensitive drum 31 to form an electrostatic
latent image thereon. Next, the toner carried on the surface of the
developing roller 25 is supplied to the latent image formed on the
photosensitive drum 31 for developing the latent image.
[0026] The fixing unit 40 includes a heating roller 41, and a
pressure roller 42. The fixing unit 40 thermally fixes a toner
image to a sheet S when the sheet S passes between the heating
roller 41 and the pressure roller 42. After the toner image has
been thermally fixed to the sheet S, the sheet S is conveyed along
a discharge path 45 and discharged onto a discharge tray 46.
[0027] The printer 1 also includes a re-conveying path 47 disposed
beneath the discharge path 45 for conveying a sheet S back to the
image-forming unit 10 after an image has been formed on one side of
the sheet S in order to form an image on the other side.
[0028] The fan 50 is provided on a side wall of the device frame 2.
More specifically, the fan 50 is disposed between the fixing unit
40 and the image-forming unit 10 with respect to the front-rear
direction (left-right direction in FIG. 1). The fan 50 functions to
lower the internal temperature of the printer 1 by exhausting air
in the device frame 2 out of the device frame 2 through a vent (not
shown).
[0029] The printer 1 is also provided with a rear cover 3 disposed
on the rear wall of the device frame 2. The rear cover 3 can be
opened and closed by pivoting about a cover shaft 3A on the rear
side of the device frame 2 near the bottom thereof. An opening in
the rear side of the device frame 2 is exposed when the rear cover
3 is opened, enabling the user to gain access to the interior of
the device frame 2.
[0030] FIG. 2 is a block diagram showing the electrical structure
of the printer 1. In its electrical configuration, the printer 1
includes a control unit 60, a booster 71, a laser drive circuit 73,
a main motor 75, a heater 77, a thermistor 79, a fan motor 81, a
cover sensor 83, a communication unit 85, and a display 87. The
thermistor 79 is an example of the temperature-detecting unit and
temperature sensor in the invention.
[0031] The booster 71 generates a high voltage to be applied to the
scorotron charger 33, the developing roller 25, and the transfer
roller 35. The laser drive circuit 73 supplies electricity to the
laser light-emitting unit.
[0032] The main motor 75 drives the rotation of rotary bodies in
the process unit 21, such as the photosensitive drum 31 and the
developing roller 25; and the rotary bodies in the paper-conveying
system, such as the feeding roller 7 and the registration rollers
9.
[0033] The heater 77 is built into the heating roller 41 for
heating the same. The thermistor 79 is disposed in proximity to the
heating roller 41 for detecting the surface temperature of the
heating roller 41 without contact. The thermistor 79 provides
feedback for regulating the surface temperature of the heating
roller 41 to a target value. The fan motor 81 functions to rotate
the fan 50. The cover sensor 83 detects when the rear cover 3 is
opened and closed.
[0034] The communication unit 85 functions to exchange data with a
data terminal device. The display 87 is configured of a liquid
crystal panel and displays various data in response to commands
from the control unit 60.
[0035] The control unit 60 includes a CPU 61, a ROM 63, and a RAM
65. The CPU 61 functions to control the image-forming unit 10, to
regulate the temperature of the fixing unit 40, and to control the
fan 50.
[0036] The ROM 63 stores various programs, and data that the CPU 61
references when executing various processes based on these
programs, such as a temperature correction coefficient .alpha., and
a temperature correction offset .beta.. The RAM 65 is used as the
main memory when the CPU 61 executes these processes.
[0037] The printer 1 has three primary modes, including a print
mode, a ready mode, and a sleep mode. The printer 1 is in the print
mode when executing a printing process. In the print mode, the
control unit 60 regulates the temperature of the fixing unit 40 at
a fixing temperature (210.degree. C., for example). In the ready
mode, the control unit 60 maintains the fixing unit 40 at a standby
temperature (160.degree. C., for example) in order to be able to
quickly execute a printing process upon receiving a print command.
The printer 1 enters the sleep mode in order to conserve power. In
the sleep mode, the control unit 60 maintains the fixing unit 40 in
an off state.
[0038] The printer 1 according to the first embodiment temporarily
shifts to the ready mode after the power has been turned on. Upon
receiving a print command, the printer 1 shifts into the print mode
to execute the printing process and shifts back to the ready mode
after completing the printing process.
[0039] If the printer 1 has been in the ready mode for a
predetermined time without receiving a print command, the printer 1
enters the sleep mode. Thus, when the printer 1 has been in the
ready mode for the predetermined time after the power was turned on
or after completing a printing process, the printer 1 then shifts
into the sleep mode. If the printer 1 receives a print command
while in the sleep mode, the printer 1 shifts into the print mode
to execute the printing process, then shifts into the ready mode
after completing the printing process.
[0040] The printer 1 employs the non-contact thermistor 79 to
detect the temperature of the fixing unit 40. A non-contact
temperature sensor has an advantage over a contact temperature
sensor in that toner or other foreign matter becoming deposited on
the surface of the fixing unit 40 will have little effect on the
temperature detection results.
[0041] However, the detection temperature of a non-contact sensor
lags behind the actual temperature of the detection target. As
shown in the graph of FIG. 3, the detection temperature of the
thermistor 79 is lower than the actual temperature of the fixing
unit 40 (surface temperature of the heating roller 41) immediately
after the heater 77 begins heating the heating roller 41.
Therefore, the control unit 60 corrects the detection temperature T
of the thermistor 79 using the temperature correction formula (1)
shown below to obtain a corrected temperature Z and uses this
corrected temperature Z as feedback for controlling the temperature
of the fixing unit 40. This enables the control unit 60 to suppress
the lag in temperature detection by the thermistor 79 in order to
control the temperature of the fixing unit 40 with high
precision.
Z=.alpha..times.T+.beta. (1)
Here, .alpha. denotes the temperature correction coefficient and
.beta. denotes the temperature correction offset.
[0042] As shown in FIG. 3, an error E denoting the difference
between the detection temperature of the thermistor 79 and the
actual temperature of the fixing unit 40 is larger at lower
detection temperatures and gradually decreases as time elapses
after heating in the fixing unit 40 is started. Accordingly, the
printer 1 of the embodiment determines the temperature correction
coefficient .alpha. and the temperature correction offset .beta. to
be used in the temperature correction formula based on the
detection temperature of the thermistor 79 at the start of heating
and the amount of time elapsed since the start of heating. The
values of the temperature correction coefficient .alpha. and
temperature correction offset .beta. are set so that the lower the
detection temperature of the thermistor 79 at the start of heating,
the greater the difference between the corrected temperature Z and
the detection temperature T. Further, the temperature correction
coefficient .alpha. and the temperature correction offset .beta.
are set so that the greater the amount of time that has elapsed
since the start of heating, the smaller the difference between the
corrected temperature Z and the detection temperature T.
[0043] The printer 1 controls the fan 50 based on the detection
temperature of the thermistor 79. When the detection temperature of
the thermistor 79 before the start of a printing operation is lower
than or equal to a threshold value (150.degree. C., for example),
the printer 1 drives the fan 50 at low speed for a prescribed time
following the start of the printing operation, then drives the fan
50 at high speed after the prescribed time has elapsed.
[0044] However, if the detection temperature is higher than the
threshold value, the control unit 60 drives the fan 50 at high
speed after the start of the printing operation. Here, "high speed"
denotes the maximum speed at which the fan motor 81 can be driven
to rotate, while "low speed" denotes one-half the maximum speed,
for example.
[0045] Next, this fan control process will be described in greater
detail with reference to the printer state transition diagram shown
in FIG. 4.
[0046] When the printer 1 receives a print job while in the sleep
mode, in which the control unit 60 is maintaining the fixing unit
40 in its off state, the control unit 60 acquires the detection
temperature of the thermistor 79 and corrects this detection
temperature using the temperature correction formula
Z=1.1.times.T+2.
[0047] Next, the control unit 60 determines which temperature range
in which the corrected temperature Z belongs from among the ranges
50.degree. C. or less, 51-100.degree. C., 101-150.degree. C., and
151.degree. C. or greater. A temperature control pattern used by
the printer 1 after receiving a print job is set for each of these
temperature ranges, as shown in FIG. 4. The printer 1 is controlled
according to the control pattern determined based on the corrected
temperature Z. Note that the fan 50 is driven at low speed for
printer states enclosed in chain lines in FIG. 4, and is driven at
high speed for states enclosed in a dashed line. The solid line
indicates the printing modes during which the printing process is
executed.
[0048] The printer 1 transitions from the sleep mode to the warm-up
mode state Warm-up A when the corrected temperature Z is less than
or equal to 50.degree. C. For Warm-up A, the control unit 60 uses
the temperature correction formula Z=1.5.times.T-6 to correct the
detection temperature of the thermistor 79 and executes a warm-up
process for increasing the temperature in the fixing unit 40 so
that the corrected temperature Z reaches the fixing temperature
(210.degree. C., for example). Once the corrected temperature Z has
risen to the fixing temperature, the printer 1 transitions to the
print mode.
[0049] In this example, the printer 1 transitions to the print mode
state Print A, as shown in FIG. 4. When transitioning to Print A,
the control unit 60 controls the image-forming unit 10 to execute a
printing process while continuing to drive the fan 50 at low
speed.
[0050] Note that Print A includes three states A-1, A-2, and A-3,
and the printer 1 transitions among these states in the order
A-1.fwdarw.A-2.fwdarw.A-3. These three states differ in the formula
that the control unit 60 uses to calculate the corrected
temperature Z. Specifically, the control unit 60 uses the
temperature correction formula Z=1.4.times.T-6 for state A-1, the
temperature correction formula Z=1.4.times.T-21 for state A-2, and
the temperature correction formula Z=1.3.times.T-11 for state A-3
to correct the detection temperature of the thermistor 79. The
control unit 60 then uses the corrected temperature Z as feedback
to control the temperature of the fixing unit 40 in order that the
corrected temperature Z can be maintained at the fixing temperature
required to thermally fix toner to the sheet S.
[0051] The execution time for Print A is set to a duration of 27
seconds. Thus, when 27 seconds have elapsed after transitioning to
Print A, the printer 1 transitions from state Print A to state
Print E. When the printer 1 enters state Print E, the control unit
60 switches the speed of the fan 50 from low speed to high speed
and controls the state at which the printer 1 executes the printing
process while driving the fan 50 at high speed. In the print mode
state Print E, the control unit 60 uses the temperature correction
formula Z=1.2.times.T-13 to correct the detection temperature of
the thermistor 79, and controls the temperature of the fixing unit
40 so that the corrected temperature Z is maintained at the fixing
temperature.
[0052] After completing the printing process, the printer 1 shifts
from the print mode to the ready mode. In the ready mode, the
printer 1 enters a standby state to wait for a print command. At
this time, the control unit 60 controls the fan 50 at low speed. In
the ready mode, the control unit 60 uses the temperature correction
formula Z=1.1.times.T+35 to correct the detection temperature of
the thermistor 79, and uses the corrected temperature Z as feedback
to control the temperature of the fixing unit 40 so that the
corrected temperature Z remains at a standby temperature lower than
the fixing temperature (160.degree. C., for example).
[0053] Further, if the printer 1 has completed the printing process
by the time 27 seconds have elapsed since shifting to state Print
A, the printer 1 transitions from state Print A to state Wait A in
the wait mode. In Wait A, the control unit 60 uses the temperature
correction formula Z=1.1.times.T-8 to correct the detection
temperature of the thermistor 79. Next, the control unit 60 turns
the heater 77 off while maintaining the fan 50 at low speed and
waits until the corrected temperature Z drops to the standby
temperature (160.degree. C., for example), which is lower than the
fixing temperature. Once 30 seconds have elapsed after the printing
process was completed, the printer 1 transitions to the ready mode.
This is because the corrected temperature Z drops generally to the
standby temperature sufficiently after 30 seconds.
[0054] The printer 1 transitions from the sleep mode to the warm-up
mode state Warm-up B when the corrected temperature Z is higher
than or equal to 51.degree. C. and less than or equal to
100.degree. C. For Warm-up B, the control unit 60 uses the
temperature correction formula Z=1.5.times.T-5 to correct the
detection temperature of the thermistor 79 and executes a warm-up
process for increasing the temperature in the fixing unit 40 so
that the corrected temperature Z reaches the fixing temperature
(210.degree. C., for example). Once the corrected temperature Z has
risen to the fixing temperature, the printer 1 transitions to the
print mode.
[0055] In this case, the printer 1 transitions to the print mode
state Print B, as shown in FIG. 4. When transitioning to Print B,
the control unit 60 controls the image-forming unit 10 to execute a
printing process while continuing to drive the fan 50 at low
speed.
[0056] Note that Print B includes three states B-1, B-2, and B-3,
and the printer 1 transitions among these states in the order
B-1.fwdarw.B-2.fwdarw.B-3. These three states differ in the formula
that the control unit 60 uses to calculate the corrected
temperature Z. Specifically, the control unit 60 uses the
temperature correction formula Z=1.4.times.T-8 for state B-1, the
temperature correction formula Z=1.3.times.T-8 for state B-2, and
the temperature correction formula Z=1.2.times.T-5 for state B-3 to
correct the detection temperature of the thermistor 79. The control
unit 60 then uses the corrected temperature Z as feedback to
control the temperature of the fixing unit 40 in order that the
corrected temperature Z can be maintained at the fixing temperature
required to thermally fix toner to the sheet S.
[0057] The execution time for Print B is set to a duration of 22
seconds. Thus, when 22 seconds have elapsed after transitioning to
Print B, the printer 1 transitions from state Print B to state
Print E. When the printer 1 enters state Print E, the control unit
60 switches the speed of the fan 50 from low speed to high speed
and controls the state at which the printer 1 executes the printing
process while driving the fan 50 at high speed.
[0058] After completing the printing process, the printer 1 shifts
from the print mode to the ready mode. In the ready mode, the
printer 1 enters a standby state to wait for a print command. At
this time, the control unit 60 controls the fan 50 at low
speed.
[0059] Further, if the printer 1 has completed the printing process
by the time 22 seconds have elapsed since shifting to state Print
B, the printer 1 transitions from state Print B to state Wait B in
the wait mode. In Wait B, the control unit 60 uses the temperature
correction formula Z=1.1.times.T-8 to correct the detection
temperature of the thermistor 79. Next, the control unit 60 turns
the heater 77 off while maintaining the fan 50 at low speed and
waits until the corrected temperature Z drops to the standby
temperature (160.degree. C., for example), which is lower than the
fixing temperature. Once 30 seconds have elapsed after the printing
process was completed, the printer 1 transitions to the ready mode.
This is because the corrected temperature Z drops generally to the
standby temperature sufficiently after 30 seconds.
[0060] The printer 1 transitions from the sleep mode to the warm-up
mode state Warm-up C when the corrected temperature Z is higher
than or equal to 101.degree. C. and less than or equal to
150.degree. C. For Warm-up C, the control unit 60 uses the
temperature correction formula Z=1.3.times.T-20 to correct the
detection temperature of the thermistor 79 and executes a warm-up
process for increasing the temperature in the fixing unit 40 so
that the corrected temperature Z reaches the fixing temperature
(210.degree. C., for example). Once the corrected temperature Z has
risen to the fixing temperature, the printer 1 transitions to the
print mode.
[0061] In this case, the printer 1 transitions to the print mode
state Print C, as shown in FIG. 4. When transitioning to Print C,
the control unit 60 controls the image-forming unit 10 to execute a
printing process while continuing to drive the fan 50 at low
speed.
[0062] Note that Print C includes three states C-1, C-2, and C-3,
and the printer 1 transitions among these states in the order
C-1.fwdarw.C-2.fwdarw.C-3. These three states differ in the formula
that the control unit 60 uses to calculate the corrected
temperature Z. Specifically, the control unit 60 uses the
temperature correction formula Z=1.2.times.T+2 for state C-1, the
temperature correction formula Z=1.2.times.T+3 for state C-2, and
the temperature correction formula Z=1.2.times.T-2 for state C-3 to
correct the detection temperature of the thermistor 79. The control
unit 60 then uses the corrected temperature Z as feedback to
control the temperature of the fixing unit 40 in order that the
corrected temperature Z can be maintained at the fixing temperature
required to thermally fix toner to the sheet S.
[0063] The execution time for Print C is set to a duration of 18
seconds. Thus, when 18 seconds have elapsed after transitioning to
Print C, the printer 1 transitions from state Print C to state
Print E. When the printer 1 enters state Print E, the control unit
60 switches the speed of the fan 50 from low speed to high speed
and controls the state at which the printer 1 executes the printing
process while driving the fan 50 at high speed.
[0064] After completing the printing process, the printer 1 shifts
from the print mode to the ready mode. In the ready mode, the
printer 1 enters a standby state to wait for a print command. At
this time, the control unit 60 controls the fan 50 at low
speed.
[0065] Further, if the printer 1 has completed the printing process
by the time 18 seconds have elapsed since shifting to state Print
C, the printer 1 transitions from state Print C to state Wait C in
the wait mode. In Wait C, the control unit 60 uses the temperature
correction formula Z=1.1.times.T-8 to correct the detection
temperature of the thermistor 79. Next, the control unit 60 turns
the heater 77 off while maintaining the fan 50 at low speed and
waits until the corrected temperature Z drops to the standby
temperature (160.degree. C., for example), which is lower than the
fixing temperature. Once 30 seconds have elapsed after the printing
process was completed, the printer 1 transitions to the ready mode.
This is because the corrected temperature Z drops generally to the
standby temperature sufficiently after 30 seconds.
[0066] The printer 1 transitions from the sleep mode to the warm-up
mode state Warm-up D when the corrected temperature Z is higher
than or equal to 151.degree. C. For Warm-up D, the control unit 60
uses the temperature correction formula Z=1.3.times.T-20 to correct
the detection temperature of the thermistor 79 and executes a
warm-up process for increasing the temperature in the fixing unit
40 so that the corrected temperature Z reaches the fixing
temperature (210.degree. C., for example). Once the corrected
temperature Z has risen to the fixing temperature, the printer 1
transitions to the print mode.
[0067] In this case, the printer 1 transitions to the print mode
state Print D, as shown in FIG. 4. When transitioning to Print D,
the control unit 60 controls the image-forming unit 10 to execute a
printing process while continuing to drive the fan 50 at high
speed.
[0068] Note that Print D includes three states D-1, D-2, and D-3,
and the printer 1 transitions among these states in the order
D-1.fwdarw.D-2.fwdarw.D-3. These three states differ in the formula
that the control unit 60 uses to calculate the corrected
temperature Z. Specifically, the control unit 60 uses the
temperature correction formula Z=1.2.times.T+2 for state D-1, the
temperature correction formula Z=1.2.times.T+3 for state D-2, and
the temperature correction formula Z=1.2.times.T-2 for state D-3 to
correct the detection temperature of the thermistor 79. The control
unit 60 then uses the corrected temperature Z as feedback to
control the temperature of the fixing unit 40 in order that the
corrected temperature Z can be maintained at the fixing temperature
required to thermally fix toner to the sheet S.
[0069] The execution time for Print D is set to a duration of 24
seconds. Thus, when 24 seconds have elapsed after transitioning to
Print D, the printer 1 transitions from state Print D to state
Print E. When the printer 1 enters state Print E, the control unit
60 maintains the speed of the fan 50 at high speed and controls the
state at which the printer 1 executes the printing process while
driving the fan 50 at high speed.
[0070] After completing the printing process, the printer 1 shifts
from the print mode to the ready mode. In the ready mode, the
printer 1 enters a standby state to wait for a print command. At
this time, the control unit 60 controls the fan 50 at low
speed.
[0071] Further, if the printer 1 has completed the printing process
by the time 24 seconds have elapsed since shifting to state Print
D, the printer 1 transitions from state Print D to state Wait D in
the wait mode. In Wait D, the control unit 60 uses the temperature
correction formula Z=1.1.times.T-8 to correct the detection
temperature of the thermistor 79. Next, the control unit 60 turns
the heater 77 off while switching the speed of the fan 50 from high
speed to low speed and waits until the corrected temperature Z
drops to the standby temperature (160.degree. C., for example),
which is lower than the fixing temperature. Once 30 seconds have
elapsed after the printing process was completed, the printer 1
transitions to the ready mode. This is because the corrected
temperature Z drops generally to the standby temperature
sufficiently after 30 seconds.
[0072] If the printer 1 receives a print job while in the ready
mode, that is, if the printer 1 receives a print job while the
control unit 60 is controlling the temperature of the fixing unit
40 at the standby temperature (160.degree. C., for example), the
printer 1 transitions from the ready mode to the print mode state
Print D, as shown in FIG. 4, and the control unit 60 controls the
printer 1 in a state for executing a printing process while driving
the fan 50 at high speed. Once 24 seconds have elapsed after the
printer 1 has transitioned to Print D, the printer 1 transitions
from the state Print D to the state Print E. Once in the state
Print E, the control unit 60 controls the printer 1 to execute a
printing process while driving the fan 50 at high speed.
[0073] After completing the printing process, the printer 1
transitions from the print mode to the ready mode. In the ready
mode, the printer 1 remains in a standby state, waiting for a print
command, while the control unit 60 controls the fan 50 at low
speed.
[0074] If the printing process is completed by the time 24 seconds
have elapsed after shifting to Print D, the printer 1 shifts from
Print D to the wait mode state Wait D. In Wait D, the control unit
60 uses the temperature correction formula Z=1.1.times.T-8 to
correct the detection temperature of the thermistor 79. Next, the
control unit 60 switches off the heater 77 while maintaining the
fan 50 at low speed and enters a wait state to wait for the
corrected temperature Z to drop to a standby temperature lower than
the fixing temperature (160.degree. C., for example). When 30
seconds have elapsed after completion of the printing process, the
printer 1 shifts to the ready mode. This is because the corrected
temperature Z drops generally to the standby temperature
sufficiently after 30 seconds.
[0075] FIGS. 5A and 5B are flowcharts illustrating the fan control
process shown in FIG. 4. The fan control process starts once the
control unit 60 transitions to the sleep mode, that is, the control
unit 60 is in the sleep mode when executing S1. In S1, the control
unit 60 determines whether a print job (print command) is received
or not. The print job is received via the communication unit 85,
for example. In S3, the control unit 60 acquires a detected
temperature T from the thermistor 79. In S5, the control unit 60
corrects the detected temperature T by the temperature correction
formula assigned with the sleep mode (Z=1.1.times.T+2) described
above, and thus obtains the corrected temperature Z. As described
above, the fan control process starts once the control unit 60
transitions to the sleep mode. However, the fan control process may
start once the control unit 60 transitions to the ready mode or the
wait mode. In this case, the warm-up mode may start directly from
the ready mode or the wait mode without executing the sleep mode.
In other words, the control unit 60 is in in the ready mode or the
wait mode when executing S1.
[0076] Through the processes S9-S21, the control unit 60 selects a
selection mode from modes A, B, C, and D based on the corrected
temperature Z. The warm-up mode and the print mode will be executed
according to the selected mode. For example, when the selection
mode is set to the mode A, the warm-up mode state Warm-up A and the
print mode state Print A will be executed in the subsequent
processes.
[0077] Specifically, in S9, the control unit 60 determines whether
the corrected temperature obtained in S5 is lower than or equal to
50.degree. C. If the corrected temperature is lower than or equal
to 50.degree. C. (S9: YES), the control unit 60 sets the selection
mode to the mode A. If the corrected temperature is higher than
50.degree. C. (S9: NO), in S13 the control unit 60 determines
whether the corrected temperature is higher than 50.degree. C., and
lower than or equal to 100.degree. C. If the corrected temperature
is higher than 50.degree. C., and lower than or equal to
100.degree. C. (S13: YES), in S15 the control unit 60 sets the
selection mode to the mode B. If the corrected temperature is
higher than 100.degree. C. (S13: NO), in S17 the control unit 60
determines whether the corrected temperature is higher than
100.degree. C., and lower than or equal to 150.degree. C. If the
corrected temperature is higher than 100.degree. C., and lower than
or equal to 150.degree. C. (S17: YES), in S19 the control unit 60
sets the selection mode to the mode C. If the corrected temperature
is higher than 150.degree. C. (S17: NO), the control unit 60 sets
the selection mode to the mode D.
[0078] After setting the selection mode in one of the processes
S11, S15, S19, and S21, in S23 the control unit 60 transitions to a
corresponding state of the warm-up mode (one of states Warm-up A-D)
from the sleep mode, according to the determined selection mode.
Here, the warm-up mode states Warm-up A, B, C, and D respectively
correspond to the selection modes A, B, C, and D. Thus, in S23 the
control unit 60 transitions to and executes one of the warm-up mode
states Print A, B, C, and D corresponding to the current selection
mode. In S25, the control unit 60 calculates a current corrected
temperature Z by using the correction formula corresponding to the
current warm-up mode state described above. Further, in S25 the
control unit 60 determines whether the current corrected
temperature Z reaches the fixing temperature (210.degree. C., for
example). The control unit 60 repeatedly executes the process S25
while the negative determination is made in S25.
[0079] If the current corrected temperature Z reaches the fixing
temperature (S25: YES), in S27 the control unit 60 transitions to
the print mode from the warm-up mode. Here, the print mode states
Print A, B, C, and D respectively corresponds to the selection
modes A, B, C, and D. In S27 the control unit 60 transitions to and
executes one of the print mode states A, B, C, and D corresponding
to the current selection mode. In the print mode, the control unit
60 executes the printing process based on the received print
job.
[0080] In S28 the control unit 60 determines whether the printing
process has completed or not. If the printing process has not been
completed (S28: NO), in S29 the control unit 60 determines whether
a prescribed time duration has elapsed. As described above, the
prescribed time duration is set to 27 seconds for Print A, 22
seconds for Print B, 18 seconds for Print C, and 24 seconds for
Print D. If the prescribed time duration has not elapsed (S29: NO),
the control unit 60 returns to the process S28. If the prescribed
time duration has elapsed (S29: YES), in S31 the control unit 60
transitions to Print E from the current print mode state. In Print
E, the control unit 60 continues the printing process. If the
printing process has been completed in Print E, the control unit
proceeds to S33.
[0081] If the control unit 60 determines that the printing process
has completed (S28: YES), in S41 the control unit 60 transitions to
the wait mode. The wait mode states Wait A, B, C, and D
respectively correspond to the selection modes A, B, C, and D. The
control unit 60 transitions to and executes one of the wait mode
states Wait A, B, C, and D corresponding to the current selection
mode. The control unit 60 executes the wait mode for 30 seconds and
subsequently proceeds to S33.
[0082] When the printing process has been completed in Print E of
S31, or when 30 seconds has elapsed in the wait mode of S41, in S33
the control unit 60 transitions to and executes the ready mode. In
S35 the control unit 60 determines whether a new print job has been
received. If the new print job has been received (S35: YES), in S43
the control unit 60 sets the selection mode to the mode D and
returns to S27. In this case, the new print job is executed in the
print mode state Print D in S27.
[0083] If the new print job has not been received (S35: NO), in S37
the control unit 60 waits until a prescribed time interval (30
seconds, for example) has elapsed. If the prescribed time interval
has elapsed (S37: YES), in S39 the control unit 60 ends the fan
control process.
[0084] Since the control unit 60 can control the fan 50 based on
the detection temperature of the thermistor 79, the printer 1 of
the embodiment can resolve the conventional problem of fan
operations affecting the fixing unit 40. Further, when the
corrected temperature Z is lower than 150.degree. C., serving as a
threshold value, the control unit 60 drives the fan 50 at low speed
for a prescribed time interval after the printing process has
begun. This method reduces the time during which the fan 50 is
operated at high speed and is a good means of noise control. On the
other hand, when the corrected temperature Z is higher than the
threshold value of 150.degree. C., the control unit 60 drives the
fan 50 at high speed following the start of the printing process,
preventing the internal temperature of the printer 1 from rising
above a temperature tolerance.
[0085] In the printer 1 of the embodiment, the prescribed time for
driving the fan 50 at low speed is set based on the detection
temperature of the thermistor 79 and, hence, can be set to a
duration that is suitable for the detected temperature.
Specifically, the execution time of Print A for cases in which the
corrected temperature Z is lower than 50.degree. C. is set to 27
seconds, the execution time of Print B for cases in which the
corrected temperature Z is between 51.degree. C. and 100.degree. C.
is set to 22 seconds, and the execution time of Print C for cases
in which the corrected temperature Z is between 101.degree. C. and
150.degree. C. is set to 18 seconds. Thus, the duration at which
the fan 50 is driven at low speed increases for lower corrected
temperatures Z. Accordingly, the duration at which the fan 50
operates at high speed can be further reduced.
[0086] Further, since the printer 1 corrects the detection
temperature of the thermistor 79 using a temperature correction
formula, the printer 1 can correct the difference between the
detection temperature of the thermistor 79 and the actual
temperature of the fixing unit 40 in order to control the
temperature of the fixing unit 40 with high precision.
[0087] Moreover, when the state of the printer 1 transitions in the
sequence Warm-up A.fwdarw.Print A-1.fwdarw.Print A-2.fwdarw.Print
A-3.fwdarw.Print E, for example, the temperature correction formula
changes in the sequence
Z=1.5.times.T-6.fwdarw.Z=1.4.times.T-6.fwdarw.Z=1.4.times.T-21.fwdarw.Z=1-
.3.times.T-11.fwdarw.Z=1.2.times.T-13. Thus, the difference between
the corrected temperature Z and the detection temperature corrected
by the temperature correction formulae grows smaller the greater
the amount of time that has elapsed after initially heating the
fixing unit 40, making it possible to control the temperature of
the fixing unit 40 with greater accuracy.
[0088] Further, if the detection temperature of the thermistor 79
is between 51.degree. C. and 100.degree. C. when the 100 receives a
print job, for example, the control unit 60 uses the temperature
correction formula Z=1.5.times.T-5 to correct the detection
temperature of the thermistor 79 during the warm-up mode. When the
detection temperature of the thermistor 79 is between 101.degree.
C. and 150.degree. C., the control unit 60 uses the temperature
correction formula Z=1.3.times.T-20 to correct the detection
temperature during the warm-up mode. Hence, the temperature
correction formulae used by the control unit 60 produce a greater
difference between the corrected temperature Z and the detection
temperature of the thermistor 79 for lower detection temperatures,
making it possible to control the temperature of the fixing unit 40
with greater accuracy.
[0089] Next, a second embodiment of the present invention will be
described with reference to the state transition diagram of FIG.
6.
[0090] Since the effects of external air on temperature
measurements are stronger when the rear cover 3 is open, the
difference between the detection temperature of the thermistor 79
and the actual temperature of the fixing unit 40 tends to be
greater. Therefore, the control unit 60 in the second embodiment
controls the fan at a constant speed after the start of a printing
operation when the rear cover 3 is open.
[0091] More specifically, the control unit 60 detects whether the
rear cover 3 is open based on an output signal received from the
cover sensor 83. If the control unit 60 detects that the rear cover
3 is open before executing a printing operation, the control unit
60 controls the printer 1 based on the state transition diagram in
FIG. 6. The dashed border in FIG. 6 indicates a high-speed region
in which the control unit 60 drives the fan 50 at high speed. Thus,
the fan speed is set to high during the print mode. Accordingly,
while the rear cover 3 is open, the control unit 60 constantly
controls the fan 50 at high speed during printing operations,
regardless of whether the detection temperature of the thermistor
79 is higher or lower than the threshold value prior to the start
of the printing operation.
[0092] Note that the fan speed is set to low for the ready mode,
the wait mode, and the warm-up mode in FIG. 6, even when the rear
cover 3 is open so as not to increase the time for driving the fan
50 at high speed more than necessary.
[0093] While the printer 1 according to the first embodiment
described earlier uses temperature correction formulae to correct
the detection temperature of the thermistor 79, the printer 1
according to the second embodiment employs two patterns of
temperature correction formulae, with one pattern accounting for
when the rear cover 3 is open and the other accounting for when the
rear cover 3 is closed. The temperature correction formulae
accounting for when the rear cover 3 is closed are employed for the
states in the transition diagram of FIG. 4, while temperature
correction formulae accounting for when the rear cover 3 is open
are employed for the states in the transition diagram of FIG. 6. In
FIG. 6, the correction formulae are shown by
".alpha..times.T+.beta.", but specific values of .alpha. and .beta.
are not shown. However, these specific values of .alpha. and .beta.
vary for each mode (warm-up A-D, and print A-1, A-2, for example)
similarly to FIG. 4. So, in FIG. 6, the difference between the
corrected temperature Z and the detection temperature corrected by
the temperature correction formulae may grow smaller the greater
the amount of time that has elapsed after initially heating the
fixing unit 40. Further, the temperature correction formulae used
by the control unit 60 may produce a greater difference between the
corrected temperature Z and the detection temperature of the
thermistor 79 for lower detection temperatures. In this way, the
difference between the detection temperature of the thermistor 79
and the actual temperature of the fixing unit 40 can be corrected,
even when the rear cover 3 is open, thereby controlling the
temperature of the fixing unit 40 with high accuracy.
[0094] For example, when the printer 1 according to the second
embodiment detects a change in the open/closed state of the rear
cover 3 while executing a printing operation according to one state
transition diagram, the printer 1 shifts to another state
transition diagram and continues the printing process. For example,
if the cover sensor 83 detects a change in the open/closed state of
the rear cover 3 when the printer 1 is in the state Print C-2 in
the transition diagram of FIG. 6, the control unit 60 transitions
from Print C-2 in this state transition diagram to Print C-2 in the
state transition diagram of FIG. 4 and continues to control the
printer 1. By switching the state of the printer 1 between two
state transition diagrams when a change in the open/closed state of
the rear cover 3 is detected during a printing process in this way,
it is possible to control the fixing unit 40 and the fan speed,
thereby achieving a state that is optimal for the open/closed state
of the rear cover 3.
[0095] Next, a third embodiment of the present invention will be
described with reference to the state transition diagram of FIG.
7.
[0096] In the first embodiment described above, the control unit 60
drives the fan 50 at low speed for a prescribed time after the
start of the printing operation when the detection temperature of
the thermistor 79 prior to the start of the printing operation is
lower than the threshold value. In the third embodiment, the
duration for driving the fan 50 at low speed is set based on the
printing speed of the printer 1.
[0097] More specifically, the printer 1 according to the third
embodiment has two modes for printing speed, including a high-speed
printing mode and a low-speed printing mode, and the user of the
printer 1 is free to select a desired mode. The user may select a
mode by performing an operation on an operating unit of the printer
1. For example, if the user has selected high-speed print as the
mode of the printer 1 prior to executing a printing operation, the
control unit 60 controls the printer 1 based on the state
transition diagram in FIG. 4 described in the first embodiment.
When the user has selected low-speed print, the control unit 60
controls the printer 1 according to the state transition diagram of
FIG. 7.
[0098] In the high-speed printing mode, the printer 1 forms images
on sheets S while conveying the sheets S at the highest possible
speed. In the low-speed printing mode, the printer 1 forms images
on sheets S while conveying the sheets S at one-half the speed of a
high-speed print. During low-speed printing, the fixing temperature
is kept lower than that during high-speed printing.
[0099] In the state transition diagram of FIG. 4, the execution
time for Print A is set to a duration of 27 seconds. Accordingly,
when the printer 1 is set to the high-speed printing mode and the
corrected temperature Z obtained by correcting the detection
temperature of the thermistor 79 prior to the start of the printing
operation is less than or equal to 50.degree. C., the control unit
60 drives the fan 50 at low speed for a duration of 27 seconds
after the start of the printing operation, then switches the fan 50
to high speed once the 27 seconds have elapsed.
[0100] On the other hand, in the state transition diagram of FIG.
6, the execution time for Print A is set to a duration of 30
seconds. Accordingly, when the printer 1 is set to the low-speed
printing mode and the corrected temperature Z obtained by
correcting the detection temperature of the thermistor 79 prior to
the start of the printing operation is less than or equal to
50.degree. C., the control unit 60 drives the fan 50 at low speed
for a duration of 30 seconds after the start of the printing
operation, then switches the fan 50 to high speed once the 30
seconds have elapsed.
[0101] In the state transition diagram of FIG. 4, the execution
time for Print B is set to a duration of 22 seconds. Accordingly,
when the printer 1 is set to the high-speed printing mode and the
corrected temperature Z obtained by correcting the detection
temperature of the thermistor 79 prior to the start of the printing
operation is higher than or equal to 51.degree. C. and less than or
equal to 100.degree. C., the control unit 60 drives the fan 50 at
low speed for a duration of 22 seconds after the start of the
printing operation, then switches the fan 50 to high speed once the
22 seconds have elapsed.
[0102] On the other hand, in the state transition diagram of FIG.
6, the execution time for Print B is set to a duration of 25
seconds. Accordingly, when the printer 1 is set to the low-speed
printing mode and the corrected temperature Z obtained by
correcting the detection temperature of the thermistor 79 prior to
the start of the printing operation is higher than or equal to
51.degree. C. and less than or equal to 100.degree. C., the control
unit 60 drives the fan 50 at low speed for a duration of 25 seconds
after the start of the printing operation, then switches the fan 50
to high speed once the 25 seconds have elapsed.
[0103] In the state transition diagram of FIG. 4, the execution
time for Print C is set to a duration of 18 seconds. Accordingly,
when the printer 1 is set to the high-speed printing mode and the
corrected temperature Z obtained by correcting the detection
temperature of the thermistor 79 prior to the start of the printing
operation is higher than or equal to 101.degree. C. and less than
or equal to 150.degree. C., the control unit 60 drives the fan 50
at low speed for a duration of 18 seconds after the start of the
printing operation, then switches the fan 50 to high speed once the
18 seconds have elapsed.
[0104] On the other hand, in the state transition diagram of FIG.
6, the execution time for Print C is set to a duration of 21
seconds. Accordingly, when the printer 1 is set to the low-speed
printing mode and the corrected temperature Z obtained by
correcting the detection temperature of the thermistor 79 prior to
the start of the printing operation is greater than or equal to
101.degree. C. and less than or equal to 150.degree. C., the
control unit 60 drives the fan 50 at low speed for a duration of 21
seconds after the start of the printing operation, then switches
the fan 50 to high speed once the 21 seconds have elapsed.
[0105] In this way, the printer 1 according to the third embodiment
sets the duration for driving the fan 50 at low speed based on the
printing speed of the printer 1, making it possible to set the
duration for driving the fan 50 at low speed to a time suited to
the printing speed. That is, since the fixing temperature is lower
in a low-speed print than in a high-speed print, the internal
temperature of the printer 1 is less likely to rise during a
low-speed print. Therefore, the duration at which the fan 50 is
driven at low speed can be increased, thereby reducing the duration
at which the fan 50 is driven at high speed.
[0106] The printer 1 according to the first embodiment described
earlier corrects the detection temperature of the thermistor 79
using temperature correction formulae. In the third embodiment, the
printer 1 employs two patterns of temperature correction formulae,
including one pattern accounting for the high-speed printing state
and one pattern accounting for the low-speed printing state. The
pattern of temperature correction formulae accounting for the
high-speed printing state is employed for each state in the
transition diagram of FIG. 4, while the pattern of temperature
correction formulae accounting for the low-speed printing state is
employed for each state in the transition diagram of FIG. 7. In
FIG. 7, the correction formulae are shown by
".alpha..times.T+.beta.", but specific values of .alpha. and .beta.
are not shown. However, these specific values of .alpha. and .beta.
vary for each mode (warm-up A-D, and print A-1, A-2, for example)
similarly to FIG. 4. So, in FIG. 7, the difference between the
corrected temperature Z and the detection temperature corrected by
the temperature correction formulae may grow smaller the greater
the amount of time that has elapsed after initially heating the
fixing unit 40. Further, the temperature correction formulae used
by the control unit 60 may produce a greater difference between the
corrected temperature Z and the detection temperature of the
thermistor 79 for lower detection temperatures. Hence, the printer
1 according to the third embodiment can correct the difference
between the detection temperature of the thermistor 79 and the
actual temperature of the fixing unit 40, whether the printing
speed is high or low, thereby controlling the temperature of the
fixing unit 40 with great accuracy.
[0107] Further, if the printing speed of the printer 1 is changed
during a printing operation, for example, the printer 1 according
to the third embodiment can continue the printing operation while
shifting to another state transition diagram. For example, if the
printing speed is modified while the printer 1 is in state Print C
of the state transition diagram shown in FIG. 7, the control unit
60 can switch the state of the printer 1 from state Print C-2 in
the transition diagram of FIG. 7 to state Print C-2 in the
transition diagram of FIG. 4 and continue controlling the printer
1.
[0108] While the invention has been described in detail with
reference to the embodiments thereof, it would be apparent to those
skilled in the art that various changes and modifications may be
made therein without departing from the scope of the invention.
[0109] (1) When the corrected temperature based on the detection
temperature of the thermistor 79 is less than a threshold value in
the first embodiment, the control unit 60 drives the fan 50 at
one-half its maximum speed for a prescribed time following the
start of a printing operation. However, the fan speed during this
prescribed time interval may be set to a speed other than one-half
the maximum fan speed, such as one-fourth or one-third the maximum
speed, provided that the fan speed is set slower than the speed
used after the prescribed time has elapsed. Alternatively, the fan
speed may be set to zero, i.e., the fan may be halted during this
prescribed time.
[0110] (2) In the first embodiment, a non-contact thermistor is
used as an example of the temperature-detecting unit, but a contact
thermistor may also be used.
[0111] (3) In the first embodiment, the detection temperature of
the thermistor 79 is corrected using a temperature correction
formula, but it is not necessary to perform temperature correction.
That is, the control unit 60 may determine whether or not to drive
the fan 50 at low speed by comparing the detection temperature of
the thermistor 79 prior to the start of a printing operation with a
threshold value.
[0112] (4) In the first embodiment, the control unit 60 includes
the CPU 61, the ROM 63, and the RAM 65. However, the control unit
60 may include one or more hardware circuit such as an application
specific integrated circuits (ASIC) in place of the CPU 61. Or, the
control unit 60 may be configured of a combination of at least one
CPU and at least one hardware circuit.
[0113] (5) The correction formulae are not limited to the formulae
explained in the above embodiments. For example, the correction
formulae are given by ".alpha..times.T+.beta.", that is, the
correction formulae are proportional to the temperature T. However,
the correction formulae may not be proportional to the temperature
T.
[0114] Further, the correction formulae for some modes may set such
that the lower the detected temperature is, the greater a
difference between the detected temperature and the corrected
temperature is. Or, the correction formulae for some modes may set
such that the longer an elapsed time from a moment when the fixing
unit 40 starts generating heat, the smaller a difference between
the detected temperature and the corrected temperature is.
[0115] (6) In the embodiments, the warm-up mode starts when a print
job is received in the sleep mode. However, the warm-up mode may
start when a print job is received in the ready mode. In this case,
the control unit 60 skips the sleep mode and executes the warm-up
mode directly from the ready mode. Further, when a print job is
received in the wait mode, the control unit 60 may skip the ready
mode and the sleep mode and start the warm-up mode directly from
the wait mode.
[0116] (7) Any configurations of the above embodiments can be
combined appropriately.
* * * * *